Spontaneous and Photoinduced Conversion of CO2 on TiO2 Anatase (001)/(101) Surfaces
High-resolution FT-IR spectroscopy was used to study the kinetics of oxygen mobility between gaseous isotopically labeled (CO2)-O-18 and solid phase (TiO2)-O-16 nanocrystalline anatase (001). Analysis of the isotopic composition of the gases produced has revealed that anatase (001) calcinated at temperatures under 500 degrees C is a very weakly reactive material and exhibits a low exchange mobility of oxygen atoms between the gas phase molecules of CO2 and the TiO2 lattice. Isotope exchange is blocked by both residual HF adsorbed onto the TiO2 surface and TiOF2 impurities. The presence of TiOF2 was shown by TEM and X-ray diffraction. However, the anatase (001) sample became slightly active after annealing at temperatures higher than 500 degrees C and upon UV illumination. Nevertheless, the effective rate constant is still 3.45 times lower than that observed for the spontaneous exchange between (CO2)-O-18 and anatase (101) material calcinated at 500 degrees C.